Phosphoric acid is generally manufactured or produced by the digestion of phosphate rock with concentrated sulfuric acid in a slurry of recycled phosphoric acid. Phosphate rock contains tricalcium phosphate. During such digestion, calcium sulfate is precipitated and phosphoric acid is released. This digestion or decomposition is referred to as the attack or digestion stage or circuit of the process. During the digestion circuit, calcium sulfate crystals are nucleated and grow. The digestion circuit is followed by a separation stage to remove calcium sulfate and other impurities from the phosphoric acid. Such separation is generally by filtration. The efficiency of such separation process is significantly dependent upon the calcium sulfate crystals that have been produced in the attack tank.
The wet process phosphoric acid production is a commercially important process. The phosphoric acid produced thereby is an important raw material for the manufacture of phosphates for the fertilizer industry, and has other commercial uses. It is of great economic benefit to increase the efficiency of the wet process phosphoric acid production. Towards such end the modification of the calcium sulfate crystals in such a manner that the filtration is improved is extremely desirable in this field. Also extremely desirable is any increase in the percentage of phosphoric acid obtained from the phosphate rock during the digestion circuit.